Steven Copertino

PM Rain Exits, Storms and Cooler Weather Possible This Weekend!

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Good Evening!

After a relatively hot and humid day across the entire Northeast and Mid Atlantic regions, we have seen large-scale thunderstorm development courtesy of the mid level shortwave that we discussed back on Monday. This shortwave was located to the west of the area, and with CAPE values of around 2000-3000 j/kg^2, PWATS near 1.5″, and strong low level lapse rates, the weak amount of energy associated with the disturbance was more than enough to set off numerous showers and thunderstorms around 2pm. Due to a significant lack of vertical wind shear, these storms were not able to move all that much from where the initial updrafts formed, and thus most cells rained themselves out over time. However, when these updrafts collapsed and the rain cooled air rapidly sunk to the surface, it created new boundaries which served to provide breeding grounds for renewed storm development. In some locations we saw this happen three to even four times over, which caused serious street flooding.

In addition to the street flooding, cool/dry air aloft allowed for some of the more robust thunderstorms to develop marginal to severe hail stones, with some reports of stones reaching the 1.75″ mark! Some folks may have noticed that these storms were also producing a cooler rain than one would expect during August, and this also can be attributed to the cooler air aloft. These drops were whats know as “Big Drops” (I know, very creative) and form when an updraft just isn’t able to keep ice suspended long enough to freeze sufficiently to reach the ground as hail. However, a few thousand feet up in the atmosphere, these drops were frozen, and when they crashed into one another, they create a negatively charged particle in the atmosphere, called an electron. When enough of these electrons build up in an updraft, they connect with positively charged particles (protons) at the surface, the path they take to get to one another creates lightning! With a ton of ice in the atmosphere from numerous updrafts this afternoon, there was a very impressive amount of lightning that went up across the area. Some of this lightning even caused damage to houses and property, with some areas losing power. Otherwise, today’s storms mainly posed a very heavy rain, lightning, and gusty wind threat.

As of six o’clock this evening, most of the showers and thunderstorms that formed early this afternoon were finally beginning to wind down. Lightning activity over the area has greatly weakened over the past hour or so, and this also points towards a gradual dissipation of the rest of the thunderstorm activity. As this time, we think that the heaviest showers and thunderstorms should dissipate by sundown, with only a few lonely cells remaining thereafter. Some residual cloud cover is likely as we head into the overnight hours, and this will help to keep overnight lows rather mild, with temperatures dropping to around the low to middle 60’s.

This evenings latest regional radar. high resolution visible satellite, surface observations. and severe warnings, showing the bulk of the heavy rain dying off. This trend should continue as we head deeper into the evening (Courtesy of Simuawips)

This evenings latest regional radar. high resolution visible satellite, surface observations. and severe warnings, showing the bulk of the heavy rain dying off. This trend should continue as we head deeper into the evening (Courtesy of Simuawips)

Thursday and Beyond

Thursday should start off just as the past few days have, with any low clouds quickly burning off by the mid to late afternoon hours. This will allow afternoon temperatures to climb significantly during the afternoon hours, with highs likely reaching the middle 80’s to lower 90’s across the area. With a moist airmass in place tomorrow, we should see the region destabilize once again by the mid to late afternoon hours, similar to as we saw today. The main difference will be that tomorrow does not look to have a coherent area of forcing to initiate thunderstorm development, so any thunderstorms tomorrow afternoon will likely have to rely on convergent boundaries from local sea breezes. This activity will likely be limited to a heavy rain and lightning threat given the lack of favorable parameters for anything outside of heavy thunderstorms. Storms should gradually fade tomorrow evening, leaving generally mild and humid conditions in their wake.

As we head into the first half of the weekend, a large shortwave trough diving out of Canada will provide a threat of heavy rain and possibly some thunderstorms over the area as moisture begins to surge north from the Gulf States. This system will be watched closely, as it does have a very favorable upper level jet streak which could potentially enhance a heavy rainfall threat over our area. A strong cold front looks to push through late Saturday and into Sunday, which should bring not only cooler temperatures to our area, but also much lower humidity compared to what we’ve been seeing-which should make for an enjoyable end to the weekend!

Now here’s a sample of what our Premium clients get with a special video discussion with Doug Simonian!

(Detailed Discussion With Doug Simonian)  

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Have a great evening!

Steve Copertino & Doug Simonian 

 

Steven Copertino

Warm and Unsettled Pattern Returns, Cool Shot This Weekend?

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Good Evening! 

Today was another beautiful day over the vast majority of the Northeast and Mid Atlantic regions as a large area of high pressure centered over the Ohio valley continues to press eastward, continues to dominate our weather. With relatively clear skies, low humidity, and warm mid level temperatures, highs today across the region were able to find their way back into the mid to upper 80’s. This is another step back up to seasonal temperatures after highs took a pretty large hit late last week and during the first half of this past weekend. These warm temperatures, clear skies, and light winds will last into the evening hours, and should be quite favorable for radiational cooling to take place during the overnight and early morning hours. This should allow low temperatures to fall into the mid to upper 60’s across the area, leading to another comfortable evening across the entire region.

As of six o’clock, there were some heavy showers and thunderstorms located over western New York and central Pennsylvania associated with a weak mid level disturbance. Shear and instability is marginal at best in this region, and as you get further from these storms, atmospheric conditions become very unfavorable to sustain these showers and thunderstorms Therefore, we do not expect any significant shower/thunderstorm activity to move into the region this evening.

This evenings latest high resolution radar mosaic, visible satellite imagery, and surface observations, showing a very nice and clear day over much of the Northeast. Some showers and thunderstorms were ongoing over portions of PA and NY. but these are expected to dissipate later this evening (Courtesy of Simuawips)

This evenings latest high resolution radar mosaic, visible satellite imagery, and surface observations, showing a very nice and clear day over much of the Northeast. Some showers and thunderstorms were ongoing over portions of PA and NY. but these are expected to dissipate later this evening (Courtesy of Simuawips)

Tuesday and Wednesday

Tuesday morning will likely start off relatively clear, with any low level clouds and residual early morning fog quickly dissipating. The area of high pressure over the Ohio Valley will continue to move to the east and get closer to the region, which should also allow for temperatures to increase a bit more as mid level ridging increases aloft. In addition to warmer mid level temperatures, the high pressure system to our south should allow winds from the west/west-southwest to take over during the day on Tuesday. This will in turn allow for dewpoints to increase to the lower to middle 60’s across the entire region, making for a more muggy feel tomorrow afternoon. Clear skies should allow for highs to quickly rise into the middle to upper 80’s tomorrow-with some locations possibly creeping into the lower 90’s.

With the increasing dewpoints over the area, instability will be on the rise, and we may have to watch for some afternoon shower and thunderstorm activity. At this time, it appears quite likely that any thunderstorm activity will likely be located over portions of Pennsylvania and New York state once again, due to an overall lack of coherent forcing, unimpressive mid level lapse rates, and weak shear values over the NYC metro area. As we head into the evening hours tomorrow, things should remain quite warm as the increased mid level moisture/temps really put a cap on any potential radiational cooling. Lows will likely be stuck in the low to middle 70’s, with more humid conditions taking over. Some patchy fog may try to develop near coastal locations, but widespread fog is not likely at this time.

On Wednesday, we can expect yet another sunny start to the day with any early morning clouds and fog quickly burning off by the late morning hours. A weak shortwave trough in the mid levels of the atmosphere will be loving to our west during the afternoon hours, and this trough will have to be watched during as the area begins to destabilize on Wednesday. This afternoons model guidance is not too impressive with shear or overall forcing over our area, but a few small changes over the next 36 hours would yield some different results. At this time, it appears that capping may hold on long enough on Wednesday afternoon to allow for some weak mid level energy to pass to the west of the region, thus setting off the development of some showers and heavy thunderstorms over portions of Pennsylvania, New Jersey, New York, and Connecticut. Wind shear and lapse rates look very marginal at this time, so any storms that do form will likely be “pulse” storms that oscillate in intensity without begin able to move much. This may result in locally heavy downpours in some areas in addition to some brief gusty winds. Regardless, highs should be in the middle 80’s to lower 90’s once again on Wednesday, with another warm and humid evening on tap as well.

This afternoons RPM model showing the development of showers and thunderstorms over portions of the Mid Atlantic and Northeast on Wednesday. Overall, these showers and thunderstorms should remain below severe limits due to weak shear and poor mid level lapse rates.

This afternoons RPM model showing the development of showers and thunderstorms over portions of the Mid Atlantic and Northeast on Wednesday. Overall, these showers and thunderstorms should remain below severe limits due to weak shear and poor mid level lapse rates.

Thursday and Beyond 

Later in the week, a strong cold front associated with a large northern stream disturbance will begin to track to the south and east. Before the frontal boundary reaches the area, precipitable water values will likely surge once again, possibly edging over the 2″ mark over portions of the Mid Atlantic. This moisture surge will be similar to the one that occurred last week, but with a completely different upper level setup this time. As the front approaches the region on Friday and Saturday, there is the possibility of numerous showers and thunderstorms breaking out as the parameters for thunderstorm development become much more favorable, with a strong upper jet maximum, increased forcing, and better lapse rates. Depending on how this system evolves over the next few days, we may have to watch for another localized flooding event over portions of the NYC metro area.

As this frontal system pushes through on Saturday and Sunday, a large area of high pressure dropping down from Canada will begin to take control, which should provide a nice end to the weekend, with cooler conditions and much lower humidity. At this time, this period of mid temperatures and decreased humidity looks to last into the middle of next week, before we have to worry about our next rain chances.

This afternoons European ensembles, showing relatively good agreement on a brief cool down after a frontal passage this upcoming weekend (Courtesy of Tropical Tidbits)

This afternoons European ensembles, showing relatively good agreement on a brief cool down after a frontal passage this upcoming weekend (Courtesy of Tropical Tidbits)

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Have a great evening!

Steve Copertino

Steven Copertino

Bulk of Unusual July Storm Stays South, Locally Heavy Rain Still Possible

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Good Evening! 

Well the storm that we have been following for the past week or so is in its formative stages as of this afternoon/evening, with heavy rain beginning to break out over portions of the Mid Atlantic states. While the storm should continue to develop and mature through the evening, the overall evolution and impacts that will be accompanying this system have changed quiet a bit. As we outlined on Wednesday in the “What Could Go Wrong” section, we stated that the overall positive nature of the incoming trough was not conducive for phasing of the lead energy ahead of the system, thus making us question the overall likelihood of widespread heavy rainfall over the New York metro area. Since that time, the models have come into line with our previous thinking and have really shifted the upper level features around, which has in turn has had a rather dramatic effect on exactly where the heaviest rainfall will occur tonight and into Saturday morning.

This afternoons and evenings regional radar mosaic, high resolution visible satellite imagery, and surface observations, showing the development of widespread heavy rains over the Mid Atlantic region. This development will continue to ramp up through this evening (Courtesy of Simuawips.com)

This afternoons and evenings regional radar mosaic, high resolution visible satellite imagery, and surface observations, showing the development of widespread heavy rains over the Mid Atlantic region. This development will continue to ramp up through this evening (Courtesy of Simuawips.com)

So what has changed over the past few days? 

For starters, a positively tilted trough approaching the Northeast is never really a great start if you’re looking for a large, lumbering system with abundant precipitation to form off the coast. This is exactly what we have approaching the area this evening, as noted on the latest 500mb analysis as well as water vapor imagery from the non-operational GOES-16 satellite. The next factor preventing this region from seeing a long-duration system is the very fast flow out to the east of the main storm system. This is something that we usually have to deal with when forecasting winter storms, but it also applicable to summer storms as well. This speedy flow can be attributed to a large upper level low in the eastern regions of Canada. As energy in the base of the large upper level system over Canada begins to rotate and shift southeast, it begins to flatten heights to the east out, and this is the exact opposite of what we would need to slow this system down.

Ideally, we would want the Canadian system to be centered more to the west, mitigating the effects of lower heights ahead of the storm, which would allow the system to slow down a bit and have more northward progression. So putting these negative factors all together, we can expect the shortwave over the Ohio Valley to continue to move east quite slowly, and continue to cause the development heavy rainfall over portions of the Mid Atlantic. Instead of amplifying and strengthening to our south and east tomorrow, the mid level system will remain to our west and will likely wind up getting sheared out-which should cause the overall system to decay.

This afternoons NAM, showing the mid level evolution of the storm system over the next two days. Note the lack of phasing and eventual sheared-out look

This afternoons NAM, showing the mid level evolution of the storm system over the next two days. Note the lack of phasing and eventual sheared-out look!

So what are the impacts? 

Despite its obvious flaws, this is definitely an anomalous system for this time of year and it will bring some heavy impacts, but those do not look to be directly aimed at the NYC metro area. As precipitation continues to break out later this evening, they will be in an extremely moist environment characterized by PWATS over two inches in some spots. Additionally, soundings over the Mid-Atlantic region indicate that a deep “skinny” CAPE profile also exists with values around 1500-2300j/kg^2, which will add to the torrential downpour situation as the night goes on. The last major player that is on the table, is an extremely impressive upper level jet nosing in from the the Ohio Valley. As the wind maximum from this upper level jet streak begins to move further east, it will begin to greatly expand the amount of upper level divergence, which will be directly over the heaviest areas of convection (thunderstorms). This strong upper level divergence will support whats known as low level convergent boundaries-which could spark heavy storms with prolific and near-record rainfall rates over portions of the Mid Atlantic.

It is quite obvious that the numerous favorable factors are coming together in just the right manner so that flooding concerns will be extremely high for the MA region. In fact, the Weather Prediction Center has issued a rare High Risk for flooding over portions of the Mid Atlantic! In general, rainfall totals should be around the 2-5″ range, with some localized amounts of 7-10″ possible in the heaviest of rain bands. This will almost certainly create very serious flooding, so please stay tuned to your local NWS!

Further north for the NYC metro area, things will be a bit more tame as we appear to be on the northern fringes of this system. This does not mean that we are exempt from seeing any heavy rains at all, as we will still have a very moist air mass to work with, and the same excellent upper level divergence to promote some convergent boundaries-which may spark some showers and storms. However, we will have to deal with some sinking air over the NYC area, which should prevent any widespread heavy rain from developing. Some isolated pockets of 1-2″ may be possible with the heaviest showers here, but general totals should be around an inch or less.

By tomorrow afternoon, the disturbance should begin to decay and get sheared out, which should gradually put an end to the heavy precipitation across the entire region.

(Again, if you are located in an area prone to flash flooding, please be aware of any warnings issued-ESPECIALLY during the overnight hours) 

Loop of the development and progression of the heavy rain over the Mid Atlantic over the next day and a half

Loop of the development and progression of the heavy rain over the Mid Atlantic over the next day and a half

We will be back Monday with a look at next week and beyond!

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Have a great weekend!

Steve Copertino

John Homenuk

We’re changing the way our products are structured

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Hello friends! As always, we hope this post finds you well, and we’re grateful that you’ve taken the time to read it. We’re reaching out to all of our readers and existing clients today to make you aware of a change to our company which we believe everybody will be excited about.

Over the past several months, we have taken some time to mull over the way we deliver our forecasts. Our number one priority has always been getting the forecast right, and doing so by communicating to the best of our ability. A close second priority has, and will continue to be, forecasting in a way where we bridge the gap in our readers understanding of the atmosphere. In other words, our forecasts are specifically designed and tailored not just to deliver information, but to elaborate on why things are happening, how they are happening, and what our concerns and uncertainties are.

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